Treatment of influenza

ABSTRACT

The present invention provides a double-stranded RNA which inhibits replication of influenza B viruses by RNA interference, in which the double-stranded RNA comprises an RNA having 19 to 25 nucleotides homologous with a part of an mRNA transcribed from a genomic RNA of the influenza B viruses and an antisense RNA thereof.

CROSS REFERENCE TO RELATED APPLICATION

This application is a National Stage of International Application No. PCT/JP2008/062001, filed Jul. 2, 2008, which claims priority from Japanese Patent Application No. 2007-175575, filed Jul. 3, 2007, the contents of all of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a double-stranded RNA, hairpin RNA, and a vector, as well as a pharmaceutical composition, an anti-influenza virus agent, and a detection kit for influenza B viruses containing the double-stranded RNA, the hairpin RNA, and the vector.

SEQUENCE LISTING

The instant application contains a Sequence Listing which has been submitted via EFS-Web and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Jun. 21, 2010, is named Q116600.txt and is 395,320 bytes in size.

BACKGROUND ART

Influenza is one of the infectious diseases most widely spread all over the world, and 250,000 to 500,000 people die of the disease annually. In Japan, 5 to 15% of the population contract influenza annually, and there are cases in which aged individuals or immunocompromised patients who have contracted influenza are complicated with pneumonia and result in death.

Influenza viruses are classified into three groups, namely type A, type B, and type C, based on differences in the antigenicity of protein which constructs a virus particle. Among them, type A and type B are mainly the ones which cause an infection in humans and circulate repeatedly every winter.

Influenza vaccines are used to prevent influenza. Attenuated live vaccines (i.e., in which attenuated viable pathogens are employed), inactivated vaccines (i.e., in which pathogens which lost infectivity after being subjected to inactivation treatment are employed), and component vaccines (i.e., in which purified specific components of pathogens are employed) are used worldwide, among which only component vaccines are practically used in Japan for prevention of influenza viruses.

A strain which is likely to prevail in a current year is predicted based on information of the influenza virus strain which circulated in the previous season, genetic information of the influenza viruses concurrently isolated in other countries, the prevalence of antibody for an influenza virus strain in the population, and the like, and influenza vaccines are produced based on the prediction.

Treatment methods of influenza include pharmacotherapy using an anti-influenza virus agent, and amantadine and a neuraminidase inhibitor (i.e., oseltamivir and zanamivir) are approved as anti-influenza virus agents in Japan (Non-Patent Document 1).

Meanwhile, RNAi (i.e., abbreviation of RNA interference) was found as a means for inhibiting expression of a specific gene in recent years. RNA interference refers to a biological phenomenon of inhibition of expression of a target gene, in which an mRNA, which is a transcription product of a target gene, is specially cleaved by a double-stranded RNA homologous with a specific region of the target gene at a site homologous with the double-stranded RNA (Patent Document 1).

In mammalian cells, introduction of a long-chain double-stranded RNA into a cell induces interferon and causes apoptosis. However, it has been elucidated that an mRNA of a target gene is specifically cleaved without causing apoptosis and thus a function of the target gene can be inhibited by introduction of a short-chain double-stranded RNA having 21 to 23 bp into a cell (Patent Document 2). Here, a short-chain double-stranded RNA which causes RNA interference in mammalian cells is called siRNA (i.e., abbreviation of small interfering RNA).

-   Patent Document 1: WO1999/32619 -   Patent Document 2: WO2001/075164 -   Non-Patent Document 1: Norio SUGAYA, Japanese Journal of Clinical     Medicine, 2006, vol. 64, p. 1840-1844

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, accurate prediction of an epidemic strain of influenza viruses is extremely difficult, and the current situation is that when prediction of an epidemic strain is missed, an effect of an influenza vaccine is markedly reduced.

In addition, even if prediction of an epidemic strain comes true, there are cases in which side effects such as pyrexia, rash, convulsion, anaphylactic shock, and hepatic function disorder develop with administration of an influenza vaccine, and they are fatal in a worst-case scenario.

Furthermore, amantadine is an anti-influenza virus agent which targets M2 protein of influenza A viruses, therefore, it is ineffective for influenza B viruses which do not have M2 protein. Meanwhile, a neuraminidase inhibitor is subtly effective for influenza B viruses, whilst it poses a problem of serious side effects. In sum, there is no effective treatment method for influenza B viruses compared with influenza A viruses in the current situation.

In view of the foregoing, an object of the present invention is to treat and prevent an infection caused by influenza B viruses by inhibiting replication of a wide range of influenza B virus strains.

Means for Solving the Problems

In order to achieve the object, the present invention provides a double-stranded RNA which inhibits replication of influenza B viruses by RNA interference, in which the double-stranded RNA comprises an RNA having 19 to 25 nucleotides homologous with a part of an mRNA transcribed from a genomic RNA of influenza B viruses and an antisense RNA thereof.

The present inventors found that double-stranded RNA comprising RNA having 19 to 25 nucleotides homologous with a part of an mRNA transcribed from a genomic RNA of influenza B viruses and an antisense RNA thereof inhibited replication of influenza B viruses, and further found that an infection caused by influenza B viruses could be effectively treated and prevented by introducing the double-stranded RNA into mammalian cells.

The mRNA is preferably a mRNA of an NP protein gene, an RNA polymerase PA subunit gene, an RNA polymerase PB1 subunit gene, or an RNA polymerase PB2 subunit gene.

By introducing a double-stranded RNA comprising RNA having 19 to 25 nucleotides homologous with a part of an mRNA transcribed from an NP protein gene, an RNA polymerase PA subunit gene, an RNA polymerase PB1 subunit gene, or an RNA polymerase PB2 subunit gene and antisense RNA thereof into a cell, an mRNA expressed by transcription of these genes is specifically cleaved by RNA interference, thereby replication of influenza B viruses can be inhibited.

The RNA is preferably selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 or selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 in which 1 to 3 nucleotide(s) is/are substituted. Among them, it is more preferably selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 11 or selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 11 in which 1 to 3 nucleotide(s) is/are substituted.

Introduction of double-stranded RNA consisting of any one of RNA having a nucleotide sequence as set forth in SEQ ID NOs: 1 to 57 and antisense RNA thereof into a cell can inhibit replication of influenza B viruses more strongly by RNA interference. Also, introduction of double-stranded RNA consisting of any one of RNA having a nucleotide sequence as set forth in SEQ ID NOs: 1 to 11 and antisense RNA thereof into a cell can inhibit replication of a much wider range of influenza B virus strains.

The double-stranded RNA preferably has a S/N ratio of 3 or greater in screening of double-stranded RNA by a transfection microarray using B/Johannesburg/5/99 strain.

A double-stranded RNA having a S/N ratio of 3 or greater can cleave mRNA more specifically by RNA interference.

The RNA can contain one or more modified ribonucleotide(s), and a 2′-OH group of a ribose ring is preferably substituted with a fluoro group, a methyl group, a methoxyethyl group, or a propyl group in the modified ribonucleotides. Also, one or more phosphodiester bond(s) in the RNA can be substituted with phosphorothioate bond(s).

RNA introduced into a cell can be degraded by intracellular ribonucleases, however, an RNA chain modified as above gains resistance to the ribonucleases and therefore can efficiently exert an RNA interference activity.

The double-stranded RNA can form blunt ends, however, it preferably forms overhanging ends by having DNA or RNA of 1 to 4 nucleotide(s) attached to 3′ ends of a sense and an antisense strands thereof.

A Double-stranded RNA forming overhanging ends has a stronger RNA interference activity so that it can inhibit replication of influenza B viruses more remarkably.

In addition, the present invention provides a hairpin RNA which forms the double-stranded RNA in a cell, in which an RNA homologous with a part of an mRNA transcribed from a genomic RNA of influenza B viruses is linked to antisense RNA thereof by a linker sequence.

It is not necessary to anneal two kinds of single-stranded RNA to form a double-stranded RNA in order to create the hairpin RNA because it can be created from one kind of RNA through chemical synthesis and the like, and thus handling of the hairpin RNA is easy. Furthermore, because the hairpin RNA forms double-stranded RNA in a cell, it exerts an RNA interference activity and can inhibit replication of influenza B viruses.

The double-stranded RNA preferably inhibits all of the following influenza B virus strains: B/Johannesburg/5/99 strain, B/Shangdong/07/97 strain, B/Hong Kong/8/73 strain, B/Shanghai/361/2002 strain, and B/Victoria/2/87 strain.

Even if influenza virus strains undergo mutation, it is highly possible that double-stranded RNA which can inhibit replication of all of the influenza virus strains described above will be still effective.

The present invention provides an expression vector for a double-stranded RNA which contains a first DNA complementary to an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 or an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 in which 1 to 3 nucleotide(s) is/are substituted and a second DNA complementary to the first DNA, as well as promoters on 5′ sides of each of the first DNA and the second DNA, in which, in a cell to which the vector is introduced, the vector transcribes a first RNA complementary to the first DNA and a second RNA complementary to the second DNA, and the first RNA and the second RNA hybridize to each other to form double-stranded RNA.

Furthermore, the present invention provides an expression vector for a double-stranded RNA which contains a first DNA complementary to an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 or an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 in which 1 to 3 nucleotide(s) is/are substituted, in which the RNA has an RNA having 1 to 4 nucleotide(s) attached to a 3′ end thereof, and a second DNA complementary to an RNA which is an antisense RNA of an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 or antisense RNA of RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 in which 1 to 3 nucleotide(s) is/are substituted, in which the RNA has an RNA having 1 to 4 nucleotide(s) attached to a 3′ end thereof, as well as promoters on 5′ sides of each of the first DNA and the second DNA, in which, in a cell to which the vector is introduced, the vector transcribes a first RNA complementary to the first DNA and a second RNA complementary to the second DNA, and the first RNA and the second RNA hybridize to each other to form a double-stranded RNA.

Still further, the present invention provides an expression vector for a hairpin RNA which contains a DNA strands encoding a hairpin RNA, in which an antisense DNA complementary to an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 or an antisense DNA complementary to an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 in which 1 to 3 nucleotide(s) is/are substituted is linked to a DNA complementary to the antisense DNA by a linker sequence, as well as promoters on 5′ sides of the DNA strands, in which, in a cell to which the vector is introduced, the vector transcribes the hairpin RNA, and the hairpin RNA is processed inside the cell to form a double-stranded RNA.

When the vector is introduced into a cell, a double-stranded RNA causing RNA interference is continuously transcribed within the cell, thereby replication of influenza B viruses can be inhibited for a long term.

The vector is preferably a plasmid vector or a viral vector to efficiently express a double-stranded RNA in mammalian cells.

Also, the double-stranded RNA, the hairpin RNA, or the vector can be used as a pharmaceutical composition or an anti-influenza virus agent because it can inhibit replication of influenza B viruses when introduced into mammalian cells.

The pharmaceutical compositions or the anti-influenza virus agents can contain a plurality of the double-stranded RNA, the hairpin RNA, or the vector. As shown in Examples, in some cases no effect is exerted on certain kinds of virus strains depending on a sequence of double-stranded RNA, however, there are cases in which an effect can be exerted on such strains by employing a plurality of double-stranded RNA concurrently.

Also, as shown in Examples, in some cases an effect diminishes over time when one of double-stranded RNA is used, however, there are cases in which an effect sustains for a longer period of time by employing a plurality of double-stranded RNA concurrently.

Furthermore, the double-stranded RNA or the hairpin RNA, or double-stranded RNA produced from the vector has an activity to specifically cleave an mRNA derived from influenza B viruses so that a kit containing the double-stranded RNA, the hairpin RNA, or the vector, and a transfection reagent can be used as a detection kit for influenza B viruses.

The pharmaceutical compositions or the anti-influenza virus agents can further contain a double-stranded RNA which inhibits replication of influenza A viruses by RNA interference.

The above-described pharmaceutical compositions or the anti-influenza virus agents can exert their therapeutic effects regardless of if infectious pathogens are influenza A viruses or influenza B viruses, and therefore even if superinfection due to a simultaneous infection with both strains occur, it can still be treated.

Effect of the Invention

An infectious disease caused by influenza B viruses can be effectively treated and prevented by introducing the double-stranded RNA, the hairpin RNA, and the vector of the present invention into mammalian cells. Furthermore, the double-stranded RNA of the present invention has an activity to inhibit replication of plural kinds of influenza B virus strains, therefore, in a case if influenza B viruses having mutation in a sequence targeted by the double-stranded RNA arise, mRNA derived from the viruses are still cleaved and replication of the influenza B viruses can be inhibited. For this, even when an epidemic strain of influenza B viruses is unknown, a therapeutic effect can be exerted on an infectious disease caused by influenza B viruses.

The pharmaceutical compositions and the anti-influenza virus agents of the present invention can contain two or more kinds of double-stranded RNA at the same time. For example, at least one kind of double-stranded RNA designed to target influenza A viruses and at least one kind of double-stranded RNA designed to target influenza B viruses can be used concurrently. This way of usage enables application of the pharmaceutical compositions of the present invention regardless of if infectious pathogens are influenza A viruses or influenza B viruses, and even if superinfection due to a simultaneous infection with both strains is caused, it can still be treated. For another example, at least two or more kinds of double-stranded RNA designed to target influenza B viruses can be used concurrently. This way of usage can expand and enhance an effect of double-stranded RNA in a case in which infectious pathogens are influenza B viruses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows steps of screening of double-stranded RNA which inhibits replication of influenza B viruses by a transfection microarray;

FIG. 2 (A) shows inhibition rates of double-stranded RNA NP-1496 alone, B-NP-1999-13 alone, as well as a combination of NP-1496 and B-NP-1999-13 for influenza virus B/Johannesburg/5/99 strain, and (B) shows inhibition rates of double-stranded RNA NP-1496 alone, B-NP-1999-13 alone, and a combination of NP-1496 and B-NP-1999-13 for influenza virus A/PR/8/34 strain;

FIG. 3 (A) shows inhibition rates of double-stranded RNA B-PB2-1997-7 alone, B-PB1-1999-1 alone, as well as a combination of B-PB2-1997-7 and B-PB1-1999-1 for influenza virus B/Shanghai/361/2002 strain, and (B) shows inhibition rates of double-stranded RNA B-PB2-1997-7 alone, B-PB1-1999-1 alone, as well as a combination of B-PB2-1997-7 and B-PB1-1999-1 for influenza virus B/Shangdong/07/97 strain; and

FIG. 4 (A) shows inhibition rates of double-stranded RNA B-NP-1999-3 alone, B-NP-1999-13 alone, as well as a combination of B-NP-1999-3 and B-NP-1999-13 for influenza virus B/Shanghai/361/2002 strain in 18-hour culture, and (B) shows inhibition rates of double-stranded RNA B-NP-1999-3 alone, B-NP-1999-13 alone, as well as a combination of B-NP-1999-3 and B-NP-1999-13 for influenza virus B/Shangdong/07/97 strain in 18-hour culture, and (C) shows inhibition rates of double-stranded RNA B-NP-1999-3 alone, B-NP-1999-13 alone, as well as a combination of B-NP-1999-3 and B-NP-1999-13 for influenza virus B/Shanghai/361/2002 strain in 30-hour culture, and (D) shows inhibition rates of double-stranded RNA B-NP-1999-3 alone, B-NP-1999-13 alone, as well as a combination of B-NP-1999-3 and B-NP-1999-13 for influenza virus B/Shangdong/07/97 strain in 30-hour culture.

DESCRIPTION OF SYMBOLS

1 . . . spot position, 2 . . . spotter, 3 . . . glass slide, 4 . . . double-stranded RNA microarray, 5 . . . cell suspension, 6 . . . petri dish, 7 . . . influenza B virus solution, 8 . . . stained double-stranded RNA microarray

BEST MODES FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention are described hereinbelow.

A double-stranded RNA of the present invention is described.

The double-stranded RNA of the present invention is characterized by being double-stranded RNA which inhibits replication of influenza B viruses by RNA interference, in which the double-stranded RNA comprises an RNA having 19 to 25 nucleotide(s) homologous with a part of an mRNA transcribed from a genomic RNA of influenza B viruses and antisense RNA thereof.

The phrase “inhibits replication of influenza B viruses by RNA interference” does not mean directly inhibiting synthesis of protein which constructs influenza viruses but it means inhibiting by cleaving an mRNA of a target viral gene sequence-specifically, and it includes transient inhibition of viral replication.

The above statement similarly applies to a case in which a double-stranded RNA “inhibits replication of influenza A viruses by RNA interference.”

“RNA” is one of the nucleic acids and it refers to a polymer of ribonucleotides consisting of ribose, phosphoric acid, and bases (i.e., adenine, guanine, cytosine, or uracil). RNA can take structure of single-stranded, double-stranded, or hairpin RNA because it can form a complementary hydrogen bond similarly to DNA.

An RNA can be synthesized based on a conventional synthetic method. For example, it can be synthesized by a nucleic acid synthesizing machine or by transcribing a DNA template in vitro (i.e., in vitro transcription). At that time a mixed group of short double-stranded RNA having 19 to 25 bp can be obtained by subjecting long double-stranded RNA synthesized in advance to dicer enzyme treatment.

The term “influenza B viruses” refers to RNA viruses which belong to orthomyxoviridae and infect humans to cause influenza. Influenza B viruses have viral genes encoding hemagglutinin (HA), neuraminidase (NA), NB protein (NB), RNA polymerase PA subunit (PA), RNA polymerase PB1 subunit (PB1), RNA polymerase PB2 subunit (PB2), M1 protein (M1), BM2 protein (BM2), NP protein (nuclear protein; NP), and NS protein (nonstructural protein; NS) in RNA genome which is consisted of negative-strand, single-stranded RNA.

When influenza B viruses infect humans, mRNA of each viral gene is transcribed from a genomic RNA template by the viruses' own RNA-dependent RNA polymerases, followed by synthesis of each viral protein by ribosomes of a host cell. Then, a set of viral genome which has been replicated through a different pathway and the viral protein thus produced assembles within the cell, thereby a virus particle is replicated. As described above, the translation products of the viral gene are essential for replication of influenza B viruses, and an infection caused by influenza B viruses can be treated or prevented, if expression of the gene is inhibited.

The double-stranded RNA is produced by synthesizing RNA having 19 to 25 nucleotides which are homologous with a part of an mRNA of a hemagglutinin (HA) gene, a neuraminidase gene, a NB protein gene, an RNA polymerase PA subunit gene, an RNA polymerase PB1 subunit gene, an RNA polymerase PB2 subunit gene, a M1 protein gene, a BM2 protein gene, an NP protein gene, and a NS protein gene of influenza B viruses as well as an antisense RNA thereof each separately, and annealing the RNA thus synthesized.

In order to strongly inhibit replication of influenza B viruses, a target mRNA is preferably an mRNA of an NP protein gene, an RNA polymerase PA subunit gene, an RNA polymerase PB1 subunit gene, or an RNA polymerase PB2 subunit gene of influenza B viruses, among which it is more preferably an mRNA of an NP protein gene.

Nucleotide sequences of each influenza B viral gene is open to the public by genetic database such as GenBank, and an RNA which constructs double-stranded RNA can be designed based on such available nucleotide sequence information.

The RNA is preferably selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 or selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 in which 1 to 3 nucleotide(s) is/are substituted, and it is more preferably selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 11 or selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 11 in which 1 to 3 nucleotide(s) is/are substituted.

The nucleotide sequences shown in SEQ ID NOs: 1 to 57 are a partial sequence of an mRNA of an NP protein gene, an RNA polymerase PA subunit gene, an RNA polymerase PB1 subunit gene, and an RNA polymerase PB2 subunit gene of influenza B viruses, and RNA which constructs double-stranded RNA can be designed based on the nucleotide sequence information of the above genes.

The RNA can contain one or more modified ribonucleotide(s) to attain resistance to degradation by ribonucleases, and a ribonucleotide in which 2′-OH group of a ribose ring is substituted with a fluoro group, a methyl group, a methoxyethyl group, or a propyl group is exemplified as the modified nucleotide.

A ribose ring which is to undergo substitution can be pyrimidine, purine, or a combination thereof. Among them, pyrimidine, for example, cytosine, a cytosine derivative, uracil, a uracil derivative, or a combination thereof is preferred. Either of a sense RNA strand and an antisense RNA strand, or both RNA strands of a double-stranded RNA can contain the modified ribonucleases to protect an RNA from degradation by ribonucleases.

One or more phosphodiester bond(s) of an RNA can be substituted with phosphorothioate bond(s) to make the RNA resistant to degradation by ribonucleases.

A person skilled in the art can carry out substitution of a 2′-OH group of a ribose ring with another functional group and a phosphodiester bond with a phosphorothioate bond based on a conventional method of chemical synthesis.

An epidemic strain of influenza B viruses is broadly classified into two groups, namely B/Victoria/2/87 and B/Yamagata/16/88, according to differences in the antigenicity of hemagglutinin (HA), and a virus strain which circulates every year is a different virus strain belonging to either group. Influenza B viruses include, for example, B/Johannesburg/5/99 strain, B/Shangdong/07/97 strain, B/Hong Kong/8/73 strain, B/Shanghai/361/2002 strain, and B/Victoria/2/87 strain.

The double-stranded RNA preferably inhibits replication of two or more of the virus strains of B/Johannesburg/5/99 strain, B/Shangdong/07/97 strain, B/Hong Kong/8/73 strain, B/Shanghai/361/2002 strain, and B/Victoria/2/87 strain, all of which are influenza B viruses, more preferably inhibits replication of three or more of the virus strains, and even more preferably inhibits replication of all of the virus strains.

The double-stranded RNA has preferably 19 to 25 bp, more preferably 19 to 23 bp, and even more preferably 19 to 21 bp in order to avoid induction of interferon and subsequent apoptosis in mammalian cells.

The double-stranded RNA of the present invention preferably forms overhanging ends by having DNA or RNA having 1 to 4 nucleotide(s) attached to 3′ ends of the sense and the antisense strands thereof, and it is more preferable that the overhanging ends are DNA or RNA consisting of 2 nucleotides. Also, the nucleotide sequence of the overhanging end of the antisense strand of the double-stranded RNA is preferably complementary to an mRNA of a target gene, however, that is not essential, and it is acceptable as long as DNA or RNA having an arbitrary nucleotide sequence is attached to a 3′ end thereof. Furthermore, the overhanging end preferably consists of DNA.

The hairpin RNA of the present invention is characterized in that it is hairpin RNA which forms the double-stranded RNA in a cell, in which an RNA homologous with a part of an mRNA transcribed from a genomic RNA of influenza B viruses is linked to antisense RNA thereof by a linker sequence. An arbitrary sequence can be used for a linker sequence as long as it does not block formation of a hairpin structure, while the linker sequence is preferably 4 to 6 nucleotides-long, more preferably 4 nucleotides-long.

Screening of double-stranded RNA which inhibits replication of influenza B viruses can be carried out by, for example, introducing double-stranded RNA into an animal cell such as an MDCK cell and subsequently infecting the cell by influenza B viruses, and observing to see if apoptosis is induced in the cell as an indication.

That is to say, if double-stranded RNA which cleaves an mRNA derived from influenza B viruses is introduced into a cell, replication of the viruses is inhibited and apoptosis will not be induced in an animal cell, even if the cell is invaded by influenza B viruses. Therefore, if the cell survives, the double-stranded RNA introduced into the cell can be judged as double-stranded RNA which inhibits replication of influenza B viruses. On the other hand, if double-stranded RNA which does not cleave mRNA derived from influenza B viruses is introduced into a cell, viruses are replicated and eventually apoptosis will be induced in the cell. Furthermore, because cells in which apoptosis is induced will die out and detach from a culture plate, an activity of double-stranded RNA which inhibits replication of influenza B viruses, which is hereinafter described as an anti-influenza virus activity, can be determined based on a ratio of viable cells adhering to the culture plate.

The screening can be carried out using a transfection microarray. A solid phase gene transfer technology of CytoPathfinder, Inc. can be employed for a system of transfection microarray, for example.

A screening using a transfection microarray starts with spotting randomly-synthesized double-stranded RNA onto a glass slide to produce a double-stranded RNA microarray. At that time a correlation between a nucleotide sequence of double-stranded RNA and a respective spot position is compiled in a database to know which double-stranded RNA is spotted on which spot position on the glass slide.

Subsequently, the double-stranded RNA microarray is placed in a petri dish and fixed thereto, to which a suspension containing MDCK cells and culture media is poured to seed the cells on the double-stranded RNA microarray. After one day of culture, the double-stranded RNA spotted on the double-stranded RNA microarray is introduced into the cells through the cell membrane. Therefore, if the cells are cultured with addition of solution containing influenza B viruses into the medium, cells which have survived without induction of apoptosis will keep adhering to specific spot positions on the double-stranded RNA microarray, while cells in which apoptosis has been induced will detach from the double-stranded RNA microarray. The double-stranded RNA having an anti-influenza virus activity can then be screened based on spot positions to which the cells are adhering as an indicator. Namely, the nucleotide sequence of double-stranded RNA having an anti-influenza virus activity can be obtained based on information of the spot position to which the cells are adhered.

The vector of the present invention is then described.

A first aspect of the vector of the present invention is characterized in that it is an expression vector for a double-stranded RNA which contains a first DNA complementary to an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 or an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 in which 1 to 3 nucleotide(s) is/are substituted and a second DNA complementary to the first DNA, as well as promoters on 5′ sides of each of the first DNA and the second DNA, in which, in a cell to which the vector is introduced, the vector transcribes a first RNA complementary to the first DNA and a second RNA complementary to the second DNA, and the first RNA and the second RNA hybridize to each other to form double-stranded RNA.

For example, a vector in which a DNA which encodes a sense strand of double-stranded RNA is linked to a first promoter in a controllable way and a DNA which encodes an antisense strand of double-stranded RNA is linked to a second promoter in a controllable way can be exemplified. In that case, the sense and the antisense strands of the double-stranded RNA are transcribed each independently, and the promoters for each strand can be identical or different from each other.

The above aspect can be an expression vector for double-stranded RNA which contains a first DNA complementary to an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 or an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 in which 1 to 3 nucleotide(s) is/are substituted, in which the RNA has an RNA having 1 to 4 nucleotide(s) attached to 3′ ends thereof, and a second DNA complementary to an RNA which is an antisense RNA of an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 or an antisense RNA of an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 in which 1 to 3 nucleotide(s) is/are substituted, in which the RNA has an RNA having 1 to 4 nucleotide(s) attached to 3′ ends thereof, as well as promoters on 5′ sides of each of the first DNA and the second DNA, and the vector transcribes a first RNA complementary to the first DNA and a second RNA complementary to the second DNA, in which the first RNA and the second RNA subsequently hybridize to each other to form double-stranded RNA in a cell to which the vector is introduced.

A second aspect of the vector of the present invention is characterized in that it is an expression vector for a hairpin RNA which contains DNA strands encoding a hairpin RNA, in which an antisense DNA complementary to an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 or an antisense DNA complementary to RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 1 to 57 in which 1 to 3 nucleotide(s) is/are substituted is linked to a DNA complementary to the antisense DNA by a linker sequence, as well as promoters on 5′ sides of the DNA strands, in which, in a cell to which the vector is introduced, the vector transcribes the hairpin RNA, and the hairpin RNA is processed inside the cell to form double-stranded RNA.

For example, a vector containing a DNA encoding a hairpin RNA, in which the DNA encoding sense and antisense strands of double-stranded RNA are linked by a linker sequence, is controllably linked to a uniform promoter can be exemplified. In that case, a single-stranded RNA, in which a sense strand and an antisense strand of double-stranded RNA are linked by a linker sequence, is produced. The sense strand part and the antisense strand part of the single-stranded RNA anneal to form hairpin RNA. An arbitrary sequence can be used for a linker sequence as long as the sequence does not block formation of a hairpin structure, while the linker sequence is preferably 4 to 6 nucleotides-long, more preferably 4 nucleotides-long.

The vector is used to create a double-stranded RNA which inhibits replication of influenza B viruses by genetic recombination technology, and it can be a vector which can transcribe a target RNA to create double-stranded RNA in a host cell. The vector can be in a form of plasmid or virus and contain an origin of replication, a terminator, a selection marker such as a neomycin resistant gene, a tetracycline resistant gene, and an ampicillin resistant gene besides a promoter, and can further contain an enhancer, a polyadenylation signal, and the like as needed.

A plasmid vector can be, for example, pcDNA3, pUC, pBR322, and pBluescript, and a viral vector can be an adenovirus, a retrovirus, a lentivirus, a baculovirus, a vaccinia virus, and the like.

A DNA to be incorporated into a vector as a template for an RNA can be synthesized by a method known in the art, and it can be inserted under control of an appropriate promoter which directs RNA transcriptional synthesis.

A promoter can be exemplified as a CMV promoter, a HSV thymidine kinase promoter, a SV40 promoter, a retroviral LTR, and a metallothionein promoter, and further, a U6 promoter or a H1 promoter, both of which are RNA polymerase III promoters. Also, the promoter can be an inducible promoter which enables alternation between “on” and “off” of expression.

A molecular biological technique necessary for construction of a vector is described in Molecular Cloning A Laboratory Manual (Sambrook, et al., Cold Spring Harbor, N.Y., 1989).

Further, the double-stranded RNA, the hairpin RNA, or the vector can be used as a pharmaceutical composition or an anti-influenza virus agent which aims to treat and prevent an infection caused by influenza B viruses.

The pharmaceutical compositions and the anti-influenza virus agents contain at least one kind of the double-stranded RNA, the hairpin RNA, or the vector as an active ingredient, and can further contain pharmaceutically acceptable additives as needed.

Also, because double-stranded RNA, the hairpin RNA, or double-stranded RNA produced from the vector can specifically cleave mRNA of a target gene of influenza B viruses, they can be used as a detection kit for influenza B viruses which exploits their such characteristic properties.

The detection kit is characterized by containing a transfection reagent in addition to the double-stranded RNA, the hairpin RNA, or the vector.

The transfection reagent can be, for example, a reagent containing lipid, in which the lipid and an objective vector form a complex, thereby the vector is introduced into a target cell. Lipid suitable for a transfection reagent can be exemplified as, for example, polyamine lipid, cationic lipid, polycationic lipid, cholesterol, neutral lipid, and cationic polyamine lipid.

The pharmaceutical composition and the anti-influenza virus agent can further contain a double-stranded RNA which inhibits replication of influenza A viruses by RNA interference. A Double-stranded RNA which inhibits replication of influenza A viruses is publicly known, and for example, ones described in the specifications of US2006/0160759 and US2006/0275265, and WO2004/028471 and WO2006/102461 can be preferably used.

EXAMPLES

The present invention is described more specifically with examples hereinbelow, however, the present invention is not limited to these examples in any way.

(Design and Synthesis of Double-Stranded RNA)

Based on nucleotide sequence information of 8 kinds of viral genes of influenza B virus B/Johannesburg/5/99 strain, which was obtained as GenBank accession nos. of CY018613 (hemagglutinin gene), CY018614 (M1 protein gene and BM2 protein gene), CY018615 (neuraminidase gene and NB protein gene), CY018616 (NP protein gene), CY018617 (NS1 protein gene and NS2 protein gene), CY018618 (RNA polymerase PA subunit gene), CY018619 (RNA polymerase PB1 subunit gene), CY018620 (RNA polymerase PB2 subunit gene), 2360 kinds of double-stranded RNA having 19 to 25 nucleotides complementary to a partial sequence of the above genes and antisense RNA thereof were designed to obtain double-stranded RNA which could cleave mRNA transcribed from the viral genes of influenza B viruses by RNA interference. Sequences of an mRNA targeted by the double-stranded RNA for RNA interference are as set forth in SEQ ID NOs: 1 to 2360.

When designing double-stranded RNA, sequences which could induce RNA interference were selected in reference to literature by Khvorova A. et al. (Cell, 2003, Vol. 115, No. 2, p. 209-216), literature by Schwarz D S. et al. (Cell, 2003, Vol. 115, No. 2, p. 199-208), literature by Hsieh A C. et al. (Nucl. Acids Res., 2004, Vol. 32, No. 3, p. 893-901), literature by Reynolds A. et al. (Nat. Biotechnol., 2004, Vol. 22, No. 3, p. 326-330) and literature by Ui-Tei K. et al. (Nucl. Acids Res., 2004, Vol. 32, No. 3, p. 936-948).

From 2360 kinds of double-stranded RNA thus designed, 80 kinds of double-stranded RNA were selected. From the selected RNA, an RNA having sequences homologous with an mRNA transcribed from viral genes of influenza B viruses, in which 2 dTTP were attached to a 3′ end thereof, and an RNA which was an antisense RNA thereof, in which 2 nucleotides of DNA complementary to the mRNA were attached to a 3′ end thereof based on the nucleotide sequence information, were each chemically synthesized. A set of an equal number of moles of the RNA and the antisense RNA thereof thus synthesized was mixed in annealing buffer (i.e., 100 mM KOAc, 2 mM MgOAc, 30 mM HEPES-KOH, pH 7.4), followed by denaturation treatment for 5 minutes at 90° C. Subsequently, annealing was carried out by incubation for one hour at 37° C., thereby double-stranded RNA was obtained.

(Method for Screening of Double-Stranded RNA by a Transfection Microarray)

FIG. 1 shows steps of screening of double-stranded RNA which inhibits replication of influenza B viruses by a transfection microarray.

A mixed solution of double-stranded RNA was prepared following steps shown in FIG. 1(A). Specifically, 25 μL of serum-free DMEM medium (i.e., Dulbecco's Modified Eagle's Medium) was put in a microtube, to which 1 to 10 μL of 100 μM double-stranded RNA was added and mixed. Subsequently, 1 to 5 μL of a transfection reagent (Lipofectamine 2000; Invitrogen Corporation) was added and mixed, and the resultant mixture was left to stand for 20 minutes. Thereafter, 10 to 200 μg of a cell-adhesion factor (fibronectin) was added to the solution in the microtube and mixed, thereby a mixed solution of double-stranded RNA used to make a double-stranded RNA microarray 4 was prepared.

As shown in FIG. 1(B), a spotter 2 was then filled with the mixed solution of double-stranded RNA and the solution was spotted on predetermined spot positions 1 laid out on a glass slide 3, thereby the double-stranded RNA microarray 4 was prepared. At that time, as a negative control, a mixed solution of the double-stranded RNA which does not inhibit replication of influenza B viruses (QIAGEN Cat. No. 1022076; it will be hereinafter described as control double-stranded RNA) was also spotted on the same glass slide 3.

As to the double-stranded RNA microarray 4 thus prepared, a correlation between the spot positions 1 and the respective sequence information of double-stranded RNA was compiled in a database to keep track ex-post facto of which double-stranded RNA having a certain nucleotide sequence was spotted on which spot position.

Thereafter, as shown in FIG. 1(B), the double-stranded RNA microarray 4 was set in a petri dish 6, to which a cell suspension 5 containing MDCK cells was poured to seed the cells. The cells were let to adhere to the double-stranded RNA microarray 4 and cultured for one day at 37° C. As a result, each double-stranded RNA spotted on the double-stranded RNA microarray 4 was to pass through the cell membrane of MDCK cells adhered to each spot position 1 to be introduced inside the cell.

Thereafter, 5 mL of influenza B virus solution 7 prepared to have a titer of 1.8×10⁷ pfu/mL was poured into the petri dish 6 and it was cultured for 23 to 47 hours at 37° C. As a result, viral replication was to occur within the MDCK cells, and cells in which apoptosis was induced was to detach from the double-stranded RNA microarray 4.

Thereafter, the double-stranded RNA microarray 4 was taken out from the petri dish 6 and washed with PBS, and surviving viable cells on the double-stranded RNA microarray 4 were fixed with ethanol. The fixed viable cells were then stained with crystal violet. A stained double-stranded RNA microarray 8 was air dried and scanned by a DNA microarray scanner (GenePix4200) to obtain a fluorescent image used for analysis of the spot positions 1 containing surviving viable cells.

The fluorescent image thus obtained was analyzed by an image analysis software (GenePix Pro Ver.6.0) to computate a total number of pixels in each of the spot positions 1. An anti-influenza virus activity and strength thereof can be evaluated based the total number of pixels because it is a value corresponding to an area of surviving cells and a number of viable cells.

Screening of double-stranded RNA by a transfection microarray was repeatedly carried out using 6 sheets of the double-stranded RNA microarray 4 in which the spot position 1 of each double-stranded RNA was differed. Then, a statistical hypothesis testing was conducted as described below between the total number of pixels in the spot position 1 of each double-stranded RNA and the total number of pixels in the spot position 1 of the control double-stranded RNA. Double-stranded RNA for which a statistical difference was confirmed in 4 or more out of 6 sheets was judged to be double-stranded RNA having an anti-influenza virus activity.

Steps of Statistical Hypothesis Testing:

1. Normalities of the total number of pixels in the spot position of the control double-stranded RNA and the total number of pixels in the spot position of each double-stranded RNA obtained through 6 sheets of the double-stranded RNA microarray were checked (W-test, level of significance of 10%). When the values of both groups were found to be in accordance with the normal distribution, differences in mean values between 2 groups were tested (proceeding to step 2). Meanwhile, when the total number of pixels of either one of the groups was not in accordance with the normal distribution, differences in measures of central tendency between 2 groups were nonparametrically tested (proceeding to step 5).

2. Homoscedasticities of the total number of pixels in the spot position of the control double-stranded RNA and the total number of pixels in the spot position of each double-stranded RNA were tested (F-test, level of significance of 25%, two-sided test). When they were homoscedastic, a Student's t-test was conducted (step 3), and when they were non-homoscedastic, a Welch's t-test was conducted (step 4).

3. Differences in mean values between the total number of pixels in the spot position of the control double-stranded RNA and the total number of pixels in the spot position of each double-stranded RNA were tested by a Student's t-test (level of significance of 1%, one-sided test).

4. Differences in mean values between the total number of pixels in the spot position of the control double-stranded RNA and the total number of pixels in the spot position of each double-stranded RNA were tested by a Welch's t-test (level of significance of 1%, one-sided test).

5. Differences in measures of central tendency between the total number of pixels in the spot position of the control double-stranded RNA and the total number of pixels in the spot position of each double-stranded RNA were tested by a Mann-Whitney's U-test (level of significance of 1%, one-sided test).

Furthermore, among the double-stranded RNA judged to have an anti-influenza virus activity, double-stranded RNA having an average S/N ratio (Signal to Noise ratio) of 3 or greater was judged to be a double-stranded RNA having a remarkable anti-influenza virus activity.

A S/N ratio described here refers to a ratio between a signal intensity obtained from a negative control (N) and a signal intensity obtained from a sample to be evaluated (S) in a screening system using a microarray, and it is used as an indication to represent strength of RNA interference effect in a screening of double-stranded RNA by a transfection microarray. Specifically, a S/N ratio is a value defined by the following formula using a mean value of the total number of pixels in the spot position of each double-stranded RNA which has been verified to have an anti-influenza virus activity by the statistical hypothesis testing (i.e., μ_(sample)), a mean value of the total number of pixels in the spot position of the control double-stranded RNA (i.e., μ_(neg)), and unbiased standard deviation (i.e., δ_(neg)). S/N ratio=μ_(sample)−μ_(neg)/δ_(neg)

The number of surviving cells in each spot position represents strength of RNA interference effect in the present screening method, therefore, how much the total number of pixels in the spot position of each double-stranded RNA which has been confirmed to have a significant difference by the statistical hypothesis testing exceeds the total number of pixels in the spot position of the control double-stranded RNA can be evaluated by a S/N ratio.

When a distribution of the total number of pixels in the spot position of the control double-stranded RNA conforms with the normal distribution, the unbiased standard deviation (δ_(neg)) corresponds to a flexion point of a normal distribution curve and 99.73% of data will be included within a range of μ_(neg)±3δ_(neg). In that case, when a detection limit of the S/N ratio is set as 3 or greater, the differences between the mean values will be 3δ_(neg) or greater according to the above formula. Therefore, it is assured that the mean value of the total number of pixels in the spot positions of the double-stranded RNA will not be included within the range of 99.73% of the distribution of the total number of pixels in the spot position of the control double-stranded RNA.

A S/N ratio was calculated after normalizing (or standardizing) the total number of pixels in the spot positions of the double-stranded RNA following the below-described steps considering that 6 sheets of the double-stranded RNA microarray were employed for investigation of the anti-influenza virus activity in the present screening method.

1. For each double-stranded RNA microarray, the total number of pixels in the spot position of each double-stranded RNA was normalized using the mean value of the total number of pixels in the spot position of the control double-stranded RNA (i.e., μ_(neg)) and the unbiased standard deviation (i.e., δ_(neg)).

2. A S/N ratio was calculated using the normalized total number of pixels in the spot position of each double-stranded RNA.

3. Double-stranded RNA of mean S/N ratio of 3 or greater was judged as double-stranded RNA having a remarkable anti-influenza virus activity.

In the above screening method, if double-stranded RNA which cleaves mRNA derived from influenza B viruses is introduced into MDCK cells, replication of the viruses is inhibited within the cells in a case when the MDCK cells is invaded by influenza B viruses, and consequently apoptosis will not be induced. Therefore, if the cells are viable and keep adhering to the spot positions 1, the double-stranded RNA introduced into the cells are judged as double-stranded RNA which inhibits replication of influenza B viruses, and it will be judged that the greater the total number of pixels in the spot position 1, the stronger the activity of inhibiting replication of influenza B viruses. On the other hand, if double-stranded RNA which does not cleave mRNA derived from influenza B viruses is introduced into MDCK cells, replication of the viruses proceeds within the cells and eventually apoptosis will be induced. Because cells in which apoptosis has been induced detach from the double-stranded RNA microarray 4, when cells detach from a spot position 1, double-stranded RNA introduced into the cells will be judged as double-stranded RNA which is not capable of inhibiting replication of influenza B viruses.

Accordingly, as long as spot positions 1 to which surviving cells are adhered are known, nucleotide sequences of double-stranded RNA having an anti-influenza virus activity is revealed by searching through the database constructed in advance.

For screening using the transfection microarray, Transfection MicroArray (trademark) of CytoPathfinder, Inc. was employed.

Example 1 Screening of Double-Stranded RNA which Inhibits Replication of Influenza B Virus B/Johannesburg/5/99 Strain

Double-stranded RNA which inhibits replication of influenza B virus B/Johannesburg/5/99 strain was screened out from 80 kinds of synthesized double-stranded RNA according to the screening method of double-stranded RNA by the transfection microarray. At that time culture time after addition of the virus strain was set as 34 hours.

Table 1 shows nucleotide sequences of antisense and sense strands of double-stranded RNA which inhibited viral replication caused by an infection with influenza B virus B/Johannesburg/5/99 strain and blocked induction of apoptosis. Double-stranded RNA which has a circle in the column titled “S/N ratio≧3” means double-stranded RNA which has an average S/N ratio of 3 or greater and a remarkable anti-influenza virus activity against viral replication.

TABLE 1 Double-stranded Nucleotide sequence  SEQ Nucleotide sequence  SEQ RNA ID of an antisense strand ID No of a sense strand ID No S/N ≧ 3 B-NP-1999-2 UUUGUUGCUUUAAUAAUCGag 2361 CGAUUAUUAAAGCAACAAAtt 2362 ○ B-NP-1999-3 UUCAUUGACAGCAUUCUUCtt 2363 GAAGAAUGCUGUCAAUGAAtt 2364 ○ B-NP-1999-4 UUAAUUGGAAUUUCAACGGga 2365 CCGUUGAAAUUCCAAUUAAtt 2366 ○ B-NP-1999-5 UUAUUUGGCCAGACCCUCCgt 2367 GGAGGGUCUGGCCAAAUAAtt 2368 ○ B-NP-1999-6 UUUAUCAUCUCUUACCAUCtt 2369 GAUGGUAAGAGAUGAUAAAtt 2370 ○ B-NP-1999-8 UUGAUGUCUCUCAAUAGCCct 2371 GGCUAUUGAGAGACAUCAAtt 2372 ○ B-NP-1999-10 UUAUCAUCUCUUACCAUCUtg 2373 AGAUGGUAAGAGAUGAUAAtt 2374 ○ B-NP-1999-11 UAAAGUUCCACCUCCUUUGat 2375 CAAAGGAGGUGGAACUUUAtt 2376 ○ B-NP-1999-12 UUGCUCUUCCUAUAAAUCGaa 2377 CGAUUUAUAGGAAGAGCAAtt 2378 ○ B-NP-1999-13 UAGGCUUGAAUUCUGUGCCtg 2379 GGCACAGAAUUCAAGCCUAtt 2380 ○ B-NP-1999-14 UUGGAUUAGGUUUCUCUCCat 2381 GGAGAGAAACCUAAUCCAAtt 2382 ○ B-NP-1999-1 UUUAAUAAGAAUAAACACCca 2383 GGUGUUUAUUCUUAUUAAAtt 2384 ○ B-NP-1999-7 UUAAUAAGAAUAAACACCCac 2385 GGGUGUUUAUUCUUAUUAAtt 2386 ○ B-NP-1999-9 UUUAAUGGUGAUCUAGGCUtg 2387 AGCCUAGAUCAGCAUUAAAtt 2388 ○ B-NP-1999-15 UUACGGAUUCGUUUGUUGCtt 2389 GCAACAAACGAAUCCGUAAtt 2390 ○ B-PA-1999-1 UUUCAGACUUAAUUCAGCCtg 2391 GGCUGAAUUAAGUCUGAAAtt 2392 B-PA-1999-2 UUCAUUUGGAUCUUAUUUGtg 2393 CAAAUAAGAUCCAAAUGAAtt 2394 B-PA-1999-3 UAAUACAUUCUUCUAUUCCag 2395 GGAAUAGAAGAAUGUAUUAtt 2396 B-PA-1999-4 UUAUUUGUGCCAUUCACUCgg 2397 GAGUGAAUGGCACAAAUAAtt 2398 ○ B-PA-1999-6 UAUUGGGUCAGUUUGAUCCcg 2399 GGAUCAAACUGACCCAAUAtt 2400 B-PA-1999-7 UUCAUUAACAAAGUAUUUCct 2401 GAAAUACUUUGUUAAUGAAtt 2402 B-PA-1999-8 UUCCAUGCUAUUUCCCAGCtt 2403 GCUGGGAAAUAGCAUGGAAtt 2404 B-PA-1999-9 UUCAUUUACUACUCUAUUGgt 2405 CAAUAGAGUAGUAAAUGAAtt 2406 ○ B-PA-1999-10 UUAACAAAGUAUUUCCUUCtt 2407 GAAGGAAAUACUUUGUUAAtt 2408 B-PA-1999-11 UUGUUCAACAAUUGCUUCCat 2409 GGAAGCAAUUGUUGAACAAtt 2410 B-PA-1999-15 UUCCAGAAUACAUUCCCUCta 2411 GAGGGAAUGUAUUCUGGAAtt 2412 ○ B-PA-1999-16 UCAUUUACUACUCUAUUGGtt 2413 CCAAUAGAGUAGUAAAUGAtt 2414 B-PB1-1999-1 UUUAGUAUAGAUCUGUUCCtt 2415 GGAACAGAUCUAUACUAAAtt 2416 ○ B-PB1-1999-3 UUAUUGGAGAACAAGACCGgt 2417 CGGUCUUGUUCUCCAAUAAtt 2418 B-PB1-1999-5 UUUAUGAGGAAACCCUUUCtg 2419 GAAAGGGUUUCCUCAUAAAtt 2420 B-PB1-1999-6 UUUAUAUUCAUCUUAAAGGct 2421 CCUUUAAGAUGAAUAUAAAtt 2422 B-PB1-1999-7 UAGCAUAUUAAACAUUCCCat 2423 GGGAAUGUUUAAUAUCCUAtt 2424 B-PB1-1999-8 UUUAUUGGAGAACAAGACCgg 2425 GGUCUUGUUCUCCAAUAAAtt 2426 ○ B-PB1-1999-9 UUGUAAAUUCAAACAUUCCag 2427 GGAAUGUUUGAAUUUACAAtt 2428 ○ B-PB1-1999-10 UAAUGAAUCAAUGAUAUCUtg 2429 AGAUAUCAUUGAUUCAUUAtt 2430 B-PB1-1999-11 UUAGAUACAAAUCCAUCUCta 2431 GAGAUGGAUUUGUAUCUAAtt 2432 ○ B-PB1-1999-13 UUCUUUAUAUUCUUUACUGag 2433 CAGUAAAGAAUAUAAAGAAtt 2434 B-PB1-1999-15 UAUUCCACUCUGGAUAUCCtg 2435 GGAUAUCCAGAGUGGAAUAtt 2436 ○ B-PB1-1999-18 UAUUCUUUCAGUCAUAGCCaa 2437 GGCUAUGACUGAAAGAAUAtt 2438 B-PB1-1999-19 UAUCUUUCUAAUGGUAUGCta 2439 GCAUACCAUUAGAAAGAUAtt 2440 B-PB1-1999-22 UUAGAUUGUACUUCAAUACta 2441 GUAUUGAAGUACAAUCUAAtt 2442 B-PB1-1999-23 UUGUUCUUUAUUAUUGUCAtt 2443 UGACAAUAAUAAAGAACAAtt 2444 B-PB1-1999-27 UUUAUUCCCAAUAAUUUACat 2445 GUAAAUUAUUGGGAAUAAAtt 2446 B-PB1-1999-28 UUGUUCCUCAAGAAUCAUGtt 2447 CAUGAUUCUUGAGGAACAAtt 2448 B-PB2-1999-5 UUUCUUACUCUUUCAACUGgg 2449 CAGUUGAAAGAGUAAGAAAtt 2450 B-PB2-1999-7 UAUUCCACCAGGUAACUGCtg 2451 GCAGUUACCUGGUGGAAUAtt 2452 ○ B-PB2-1999-10 UUUAAGUUGUAUUCCCUUGta 2453 CAAGGGAAUACAACUUAAAtt 2454 B-PB2-1999-11 UUUGAUGCGACUAUUGAUCtt 2455 GAUCAAUAGUCGCAUCAAAtt 2456 ○ B-PB2-1999-12 UUCAGUAUCUAUCACAGUCtt 2457 GACUGUGAUAGAUACUGAAtt 2458 ○ B-PB2-1999-15 UUUAACUACUUUAACGGGCtt 2459 GCCCGUUAAAGUAGUUAAAtt 2460 B-PB2-1999-16 UUUCUUAUUAUGUUAUAUUga 2461 AAUAUAACAUAAUAAGAAAtt 2462 B-PB2-1999-18 UUGUAUUCCCUUGUAUUCCaa 2463 GGAAUACAAGGGAAUACAAtt 2464

As a result, a statistical difference was confirmed between 52 double-stranded RNA and the control double-stranded RNA, of which 26 double-stranded RNA had an average S/N ratio of 3 or greater.

Example 2 Screening of Double-Stranded RNA which Inhibits Replication of Influenza B Virus Strains Other than B/Johannesburg/5/99 Strain

Among the 80 kinds of synthesized double-stranded RNA, 28 double-stranded RNA which did not exhibit an anti-influenza activity for B/Johannesburg/5/99 strain were studied to find out if any of them had an anti-influenza activity for other influenza B virus strains.

As influenza B viruses, B/Shangdong/07/97, B/Hong Kong/8/73, B/Shanghai/361/2002, and B/Victoria/2/87 strains were employed, and a test was carried out according to the method for screening of double-stranded RNA by the transfection microarray in a similar manner to Example 1.

However, because culture time needed for cell detachment to occur after addition of virus strains to a petri dish differed depending on the virus strain, the culture time after addition of virus strains was set as follows: 23 hours for B/Shangdon/07/97 strain, 36 hours for B/Hong Kong/8/73 strain, 26 hours for B/Shanghai/361/2002 strain, and 47 hours for B/Victoria/2/87 strain.

Table 2 shows nucleotide sequences of antisense and sense strands of double-stranded RNA which inhibited viral replication caused by an infection with influenza B virus B/Shangdong/07/97, B/Hong Kong/8/73, B/Shanghai/361/2002, or B/Victoria/2/87 strains and blocked induction of apoptosis. Double-stranded RNA which has a circle in the column titled “S/N ratio≧3” means double-stranded RNA which has an average S/N ratio of 3 or greater for one of the above virus strains and a remarkable anti-influenza virus activity against viral replication.

TABLE 2 Double-stranded Nucleotide sequence of SEQ Nucleotide sequence of SEQ RNA ID an antisense strand ID No a sense strand ID No S/NL ≧ 3 B-PB2-1999-2 UAAAUCUUUCAUGUCUUCCtt 2465 GGAAGACAUGAAAGAUUUAtt 2466 ○ B-PB2-1999-6 UUCAUUAAUUCAUUUAUCCca 2467 GGAUAAAUGAAUUAAUGAAtt 2468 B-PB1-1999-17 UAAGGAUUUAUAUUCAUCUta 2469 AGAUGAAUAUAAAUCCUUAtt 2470 B-PB1-1999-24 UUUCAUUUCAAUCAUUUGUtt 2471 ACAAAUGAUUGAAAUGAAAtt 2472 B-PB1-1999-26 UUCAUCUUAAAGGCUCCGCtt 2473 GCGGAGCCUUUAAGAUGAAtt 2474

As a result, a statistical difference was confirmed between 3 double-stranded RNA (B-PB2-1999-02, B-PB1-1999-17, and B-PB1-1999-26) and the control double-stranded RNA against an infection caused by B/Shangdong/07/97 strain, of which 1 double-stranded RNA (B-PB2-1999-2) had an average S/N ratio of 3 or greater. A statistical difference was confirmed between 2 double-stranded RNA (B-PB2-1999-2 and B-PB1-1999-24) and the control double-stranded RNA against an infection caused by B/Hong Kong/8/73 strain, however, neither of them had a mean S/N ratio of 3 or greater. A statistical difference was confirmed between 1 double-stranded RNA (B-PB2-1999-6) and the control double-stranded RNA against an infection caused by B/Shanghai/361/2002 strain, however, it did not have a mean S/N ratio of 3 or greater. Meanwhile, a statistical difference was not observed between any double-stranded RNA and the control double-stranded RNA against infection caused by B/Victoria/2/87 strain.

Combined with the results obtained from Example 1, 57 double-stranded RNA exhibited an anti-influenza virus activity for one of the 5 strains of influenza B viruses. Furthermore, 39 out of the 57 double-stranded RNA had a remarkable anti-influenza virus activity with a mean S/N ratio of 3 or greater for one of the virus strains. Accordingly, it was presumed that one of the 57 double-stranded RNA could inhibit viral replication and exert efficacy in treatment of influenza B viruses, even if an influenza B virus strain which is to circulate from now forward undergoes various mutations.

Example 3 Screening of Double-Stranded RNA which Inhibits Replication of a Plurality of Influenza B Virus Strains Simultaneously

Prediction of an influenza B virus strain to circulate is difficult, and even if prediction comes true, the virus is highly prone to mutation, therefore, it is presumed that if one kind of double-stranded RNA can inhibit replication of a plurality of influenza B virus strains, treatment and prevention of an infection caused by influenza B viruses are realizable. In view of the above, among the 52 double-stranded RNA which exhibited an anti-influenza virus activity for influenza B virus B/Johannesburg/5/99 strain in Example 1, double-stranded RNA further having an anti-influenza virus activity for all virus strains of B/Shangdong/07/97, B/Hong Kong/8/73, B/Shanghai/361/2002, and B/Victoria/2/87 strains was screened.

Screening was carried out according to the above-described method for screening of double-stranded RNA by the transfection microarray in a similar manner to Examples 1 and 2. In this screening, a double-stranded RNA microarray was used in which double-stranded RNA which has been reported to inhibit replication of influenza B viruses (PB1-POS and PB2-POS) was spotted to a slide as a positive control in addition to the 52 double-stranded RNA which exhibited an anti-influenza activity in Example 1. Both of PB1-POS and PB2-POS are double-stranded RNA comprising nucleotide sequences identical to PB1-2196 and PB2-1999 described in Antiviral Therapy (2006, Vol. 11, p. 431-438), and each of them was reported to cleave mRNA of an RNA polymerase PB1 subunit (PB1) gene and an RNA polymerase PB2 subunit (PB2) gene by RNA interference.

Table 3 shows double-stranded RNA IDs which inhibited viral replication caused by an infection with influenza B virus B/Johannesburg/5/99 strain, B/Shangdong/07/97 strain, B/Hong Kong/8/73 strain, B/Shanghai/361/2002 strain, and B/Victoria/2/87 strain and blocked induction of apoptosis as well as values of S/N ratio thereof.

TABLE 3 Values of S/N ratio Double-stranded B/Jonannesburg/ B/Shangdong/ B/HongKong/ B/Shanghai/ B/Victoria/ RNA ID 5/99 strain 07/97 strain 8/73 strain 361/2002 strain 2/87 strain PB1_POS 1.2 10.8 ND 3.0 ND PB2_POS 1.0 1.9 ND 1.3 ND B-NP-1999-02 11.5 29.2 9.8 19.9 8.2 B-NP-1999-03 23.6 68.0 13.9 30.4 16.5 B-NP-1999-04 32.1 82.6 8.5 30.8 7.3 B-NP-1999-05 11.4 37.0 4.1 17.9 6.1 B-NP-1999-06 27.5 78.1 16.2 37.7 16.2 B-NP-1999-08 7.5 36.7 6.8 19.4 7.5 B-NP-1999-10 20.8 61.2 12.7 31.3 14.5 B-NP-1999-11 5.9 36.0 6.1 18.4 8.7 B-NP-1999-12 9.7 42.2 7.5 21.4 3.5 B-NP-1999-13 32.2 85.2 12.2 37.8 17.5 B-NP-1999-14 14.9 56.6 8.0 5.2 8.5

As a result, out of the 52 double-stranded RNAs, a statistical difference was confirmed between 11 double-stranded RNA and the control double-stranded RNA against an infection of all virus strains of the above 5 strains, and those 11 double-stranded RNAs exhibited a remarkable anti-influenza virus activity for any of the virus strains with a mean S/N ratio of 3 or greater.

On the other hand, PB1-POS, a positive control, exhibited an anti-influenza virus activity for B/Shangdong/07/97 strain and B/Shanghai/361/2002 strain, while it hardly exhibited an anti-influenza virus activity for other virus strains.

Also, PB2-POS, another positive control, exhibited a very weak anti-influenza virus activity for B/Johannesburg/5/99 strain and B/Shangdong/07/97 strain, and it did not exhibit an anti-influenza virus activity for other virus strains.

Interestingly, it is to be noted that any one of the antisense strands of the above 11 double-stranded RNA was RNA having a sequence complementary to mRNA of NP protein.

Example 4 An Anti-Influenza Virus Activity of Double-Stranded RNA Having Mutation in a Target Sequence

Among the double-stranded RNA which has a remarkable anti-influenza virus activity for the 5 strains of influenza B viruses found in Example 3, homology between B-NP-1999-13 (sequence No. 10) and the nucleotide sequence of mRNA of the 5 virus strains were compared.

The nucleotide sequences registered in GenBank were referred to for the 4 strains other than B/Johannesburg/5/99 strain, in which an accession number for each strain was as follows: AY0441698 for B/Shangdong/7/97 strain, EF456777 for B/Hong Kong/8/73 strain, AJ784078 for B/Shanghai/361/2002 strain, and AF100359 for B/Victoria/2/87 strain.

As a result, although B-NP-1999-13 had 3 mismatched nucleotides with respect to B/Hong Kong/8/73, it exhibited a remarkable anti-influenza virus activity. Also, although it had a mismatch in a second nucleotide counting from a 5′ end of an antisense strand with respect to B/Victoria/2/87 strain, it similarly exhibited a remarkable anti-influenza virus activity.

Generally, it is said that an RNA interference activity of double-stranded RNA becomes weaker as a mismatch occurs closer to the center of a strand from the end and a number of mismatched nucleotide increases. However, B-NP-1999-13 especially had an RNA interference activity and exhibited a remarkable anti-influenza virus activity regardless of the presence of 3 mismatched nucleotides.

Based on the above results, it was suggested that even a mismatch is present, double-stranded RNA having a remarkable anti-influenza virus activity still exists depending on its nucleotide sequence. Such double-stranded RNA has an anti-influenza virus activity not only for one kind but also for plural kinds of influenza B virus strains, therefore, it was suggested that even in a case when an influenza virus strain having mutation in a sequence targeted by double-stranded RNA becomes an epidemic strain, such double-stranded RNA could fully exert a therapeutic effect for an infection caused by the strain.

Example 5 A Combinational Use of Double-Stranded RNA Designed to Target Influenza a Viruses and Influenza B Viruses

An effect for influenza viruses brought by simultaneous use of a plurality of double-stranded RNA was studied. NP-1496, which was siRNA described in WO2004/028471, was chemically synthesized as double-stranded RNA for influenza A viruses. The nucleotide sequence of NP-1496 is shown in Table 4 with the direction from a 5′ end toward a 3′ end. The 3′ ends of sense and antisense strands of NP-1496 have 2 deoxythymidine nucleotides attached thereto, and they were denoted in lowercase letters in Table 4. A set of an equal number of moles of the RNA thus synthesized and the antisense RNA thereof was mixed in annealing buffer (i.e., 100 mM KOAc, 2 mM MgOAc, 30 mM HEPES-KOH, pH 7.4), followed by denaturation treatment for 5 minutes at 90° C. Subsequently, annealing was carried out by incubation for one hour at 37° C., thereby double-stranded RNA was obtained. The above-described B-NP-1999-13 was used as double-stranded RNA for influenza B viruses.

TABLE 4 Double-stranded Nucleotide sequence of SEQ Nucleotide sequence of SEQ RNA ID an antisense strand ID No a sense strand ID No NP-1496 CUCCGAAGAAAUAAGAUCCtt 2475 GGAUCUUAUUUCUUCGGAGtt 2476

MDCK cells were suspended in RPMI1640 medium and the suspension was prepared to have 1×10⁷ cells/mL, to which NP-1496 and B-NP-1999-13 were mixed. To an electroporation cuvette having an interelectrode distance of 4 mm (product of Shimadzu Corporation), 800 μL of a mixture of the MDCK cells and the double-stranded RNA was transferred. An electrical pulse was applied with voltage of 400 V and a capacitor having capacitance of 800 μF by Shimadzu Electro Gene Transfer Equipment (GTE-10), after which the suspension was left to stand for 5 minutes on ice. The suspension thus obtained was diluted by RPMI1640 medium to be at 1×10⁶ cells/mL, and FCS was added to make a final concentration of 10%. The suspension thus obtained was seeded in a 96-well plate at 0.1 mL/well, and cultured for one day at 37° C. in the presence of 5% CO₂.

A/PR/8/34 and B/Johannesburg/5/99 were used as influenza A viruses and influenza B viruses, respectively. Each of the viruses was prepared at a concentration of 1×10⁴ pfu/mL and added at 50 μL/well to the MDCK cells into which siRNA had been introduced for virus infection. After culturing for 24 hours, the infected cells were fixed with ethanol. In order to quantitate viral protein expressed in the infected cells by ELISA, the fixed cells were blocked with 10% skim milk, after which an anti-influenza A virus nucleoprotein antibody (product of AbD serotec, MCA400) or an anti-influenza B virus nucleoprotein antibody (product of AbD serotec, MCA403) was added as a primary antibody. Subsequently, a rabbit anti-mouse IgG labeled with HRP (horse radish peroxidase) was added as a secondary antibody for recognition of the primary antibody. Then, TMB (i.e., 3,3′,5,5′-tetramethyl-benzidene), which was a substrate for HRP, was added for color development, and absorbance at a wavelength of 450 nm was measured. An inhibition rate in the wells to which siRNA was introduced was calculated by the following formula based on values obtained from a negative-control well which was not infected with viruses and a positive-control well which was infected with viruses without addition of siRNA. Inhibition rate=(absorbance of a positive-control well−absorbance of a sample well)×100/(absorbance of a positive-control well−absorbance of a negative-control well)

The results are shown in FIG. 2. As shown in FIG. 2(A), when B-NP-1999-13 was solely used at 0.1 nmol/mL, approximately 100% of an inhibitory activity was observed for B/Johannesburg/5/99 viruses. Also, as shown in FIG. 2(B), when NP-1496, which was double-stranded RNA, was solely used at 1 nmol/mL, approximately 90% of an inhibitory activity was observed for A/PR/8/34. When a mixture of these double-stranded RNA was used, an anti-virus activity was exhibited for an infection with either of the viruses, and the activity level was observed as approximately the same as when each of the double-stranded RNA was used solely.

Example 6 A Combinational Use of Double-Stranded RNA Designed to Target Influenza B Viruses and Expansion of Spectrum

B-PB2-1999-7 and B-PB1-1999-1, both of which were double-stranded RNA, were used in this test. As for viruses, B/Shanghai/361/2002 and B/Shangdong/07/97 were used. MDCK cells were mixed with the double-stranded RNA in a similar manner to Example 5, and introduction into cell was conducted by electroporation. Each of the influenza B viruses was allowed to infect after one-day culture, and a combinational effect of the double-stranded RNA was measured by quantitating viral protein present after 18 hours by ELISA using an influenza B virus antibody.

The results were shown in FIG. 3. Although B-PB2-1999-7 exhibited approximately 100% of an inhibitory activity for B/Shanghai/361/2002 when used at 0.25 nmol/mL as shown in FIG. 3(A), it exhibited as low as approximately 30% of an inhibitory activity for B/Shangdong/07/97 as shown in FIG. 3(B). Also, although B-PB1-1999-1 exhibited only approximately 20% of an inhibitory activity for B/Shanghai/361/2002 when used at 0.25 nmol/mL as shown in FIG. 3(A), it exhibited approximately 90% of an inhibitory activity for B/Shangdong/07/97 as shown in FIG. 3(B). An inhibitory activity as strong as approximately 90% or more was confirmed for either of the virus strains, when a mixture of these two kinds of double-stranded RNA was used. As shown above, it was demonstrated that there were cases in which no effect was exerted on a certain virus strain depending on a nucleotide sequence of double-stranded RNA, while an effect could be exerted on such a viral strain by combinational use of a plurality of double-stranded RNA.

Example 7 Combinational Effect of Double-Stranded RNA Designed to Target Influenza B Viruses

B-NP-1999-3 and B-NP-1999-13, both of which were double-stranded RNA, were used in this test. As for viruses, B/Shanghai/361/2002 and B/Shangdong/07/97 were used. MDCK cells were mixed with the double-stranded RNA in a similar manner to Example 5, and introduction into cell was conducted by electroporation. Each of the influenza B virus strains was allowed to infect after one-day culture, and a combinational effect of double-stranded RNA was measured by quantitating viral protein present after 18 to 30 hours by ELISA using an influenza B virus antibody.

The results were shown in FIG. 4. As shown in FIGS. 4(A) and 4(B), the two kinds of double-stranded RNA exhibited 80% or more of an inhibitory activity for both virus strains either solely or in combination in an 18-hour culture. On the other hand, as shown in FIG. 4(C), when B-NP-1999-3 and B-NP-1999-13 were each used solely at 0.1 nmol/mL and 0.05 nmol/mL, respectively, each of them exhibited only approximately 10% of an effect for B/Shanghai/361/2002 in 30-hour culture. When a mixture of these two kinds of double-stranded RNA was used, approximately 70% of an inhibitory activity was confirmed for B/Shanghai/361/2002. Also, as similarly shown in FIG. 4(D), when B-NP-1999-3 and B-NP-1999-13 were each used solely at 0.1 nmol/mL and 0.05 nmom/mL, respectively, each exhibited 50% and 0% of an inhibitory effect for B/Shangdong/07/97, respectively. Meanwhile, when a mixture of them was used, 80% of an inhibitory activity was confirmed for B/Shangdong/07/97. As shown above, it was demonstrated that there were cases in which an effect was diminished as culture time of the virus was extended with use of one kind of double-stranded RNA, however, even in such a case, the effect was sustained by using a plurality of double-stranded RNA concurrently. 

1. A double-stranded RNA which inhibits replication of influenza B viruses by RNA interference, wherein the double-stranded RNA comprises an RNA and an antisense RNA thereof, wherein the RNA is selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 4 and 5 or selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 4 and 5 in which 1 to 3 nucleotide(s) is/are substituted.
 2. The double-stranded RNA according to claim 1, which has a S/N ratio of 3 or greater in screening of double-stranded RNA by a transfection microarray using B/Johannesburg/5/99 strain.
 3. The double-stranded RNA according to claim 1, wherein the RNA optionally contains one or more modified ribonucleotide(s).
 4. The double-stranded RNA according to claim 1, wherein one or more phosphodiester bond(s) in the RNA is/are optionally substituted with phosphorothioate bond(s).
 5. The double-stranded RNA according to claim 1, which forms blunt ends.
 6. The double-stranded RNA according to claim 1, wherein the RNA is the RNA of nucleotide sequence as set forth in SEQ ID NO:4 or the RNA of nucleotide sequence as set forth in SEQ ID NO:4 in which 1 to 3 nucleotide(s) is/are substituted.
 7. A double-stranded RNA having DNA or RNA of 1 to 4 nucleotide(s) attached to 3′ ends of the sense and the antisense strands of a double-stranded RNA according to claim 6 to form overhanging ends.
 8. The double-stranded RNA according to claim 1, wherein the RNA is the RNA of nucleotide sequence as set forth in SEQ ID NO:5 or the RNA of nucleotide sequence as set forth in SEQ ID NO:5 in which 1 to 3 nucleotide(s) is/are substituted.
 9. A double-stranded RNA having DNA or RNA of 1 to 4 nucleotide(s) attached to 3′ ends of the sense and the antisense strands of a double-stranded RNA according to claim 8 to form overhanging ends.
 10. A double-stranded RNA having DNA or RNA of 1 to 4 nucleotide(s) attached to 3′ ends of the sense and the antisense strands of a double-stranded RNA according to claim 1 to form overhanging ends.
 11. A hairpin RNA which forms the double-stranded RNA according to claim 1 in a cell, wherein the RNA is linked to the antisense RNA thereof by a linker sequence.
 12. An expression vector for a double-stranded RNA which comprises a first DNA complementary to an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 4 and 5 or an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 4 and 5 in which 1 to 3 nucleotide(s) is/are substituted and a second DNA complementary to the first DNA, as well as promoters on 5′ sides of each of the first DNA and the second DNA, wherein, in a cell to which the vector is introduced, the vector transcribes a first RNA complementary to the first DNA and a second RNA complementary to the second DNA, and the first RNA and the second RNA hybridize to each other to form a double-stranded RNA.
 13. An expression vector for a double-stranded RNA which comprises a first DNA complementary to an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 4 and 5 or an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 4 and 5 in which 1 to 3 nucleotide(s) is/are substituted, wherein the RNA has an RNA having 1 to 4 nucleotide(s) attached to 3′ ends thereof, and a second DNA complementary to an RNA which is antisense RNA of an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 4 and 5 or an antisense RNA of an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 4 and 5 in which 1 to 3 nucleotide(s) is/are substituted, wherein the RNA has an RNA having 1 to 4 nucleotide(s) attached to 3′ ends thereof, as well as promoters on 5′ sides of each of the first DNA and the second DNA, wherein, in a cell to which the vector is introduced, the vector transcribes a first RNA complementary to the first DNA and a second RNA complementary to the second DNA, and the first RNA and the second RNA hybridize to each other to form a double-stranded RNA.
 14. An expression vector for a hairpin RNA which comprises DNA strands encoding a hairpin RNA, in which an antisense DNA complementary to an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 4 and 5 or an antisense DNA complementary to an RNA selected from the group consisting of RNA of nucleotide sequences as set forth in SEQ ID NOs: 4 and 5 in which 1 to 3 nucleotide(s) is/are substituted is linked to a DNA complementary to the antisense DNA by a linker sequence, as well as promoters on 5′ sides of the DNA strands, wherein, inside the cell to which the vector is introduced, the vector transcribes the hairpin RNA, and the hairpin RNA is processed in a cell to form a double-stranded RNA.
 15. A pharmaceutical composition which comprises at least one kind of a double-stranded RNA according to claim 1 as an active ingredient and one or more pharmaceutical additives.
 16. The pharmaceutical composition according to claim 15, which further comprises a double-stranded RNA which inhibits replication of influenza A viruses by RNA interference.
 17. A detection kit for influenza B viruses which comprises at least one of a double-stranded RNA according to claim 1 and a transfection reagent.
 18. A method for treatment of an infectious disease caused by influenza comprising administering to a patient in need thereof at least one kind of a double-stranded RNA according to claim 1 as an active ingredient.
 19. The method for treatment of an infectious disease caused by influenza according to claim 18, which further comprises administering to the patient a double-stranded RNA which inhibits replication of influenza A viruses by RNA interference. 